1. Field of the Invention
The present invention relates to the purification of organic polycarboxylic acids by the removal therefrom of organic monofunctional impurities. More particularly, it relates to the purification of an organic polycarboxylic acid, such as 1,4-cyclohexanedicarboxylic acid, via steam distillation, wherein organic impurities, such as 4-methyl-1-cyclohexanecarboxylic acid and cyclohexanecarboxylic acid, are removed from the polycarboxylic acid.
2. Description of the Prior Art
In U.S. Pat. No. 3,243,456, Caldwell, et al, disclose a method for purifying insoluble dicarboxylic acids wherein insoluble acids are converted into any soluble salt, such as ammonium, sodium, lithium, potassium, or amine salts, by adding bases or basic salts to a suspension of the acid, the solutions of the salts of insoluble organic acids are treated with various absorbing agents, such as activated carbons, clays, and ion exchange resins and optionally with oxidizing agents or reducing agents to convert various impurities to substances which can be removed more easily than the original form, and the insoluble acid is regenerated by treating the hot solution of the salt with a soluble acid having an ionization constant which is lower than that of the insoluble acid which is being purified, which will cause the insoluble acid to form large, uniform crystals of pure acid.
In U.S. Pat. No. 3,646,124, Johnson, et al, disclose an extraction process for the removal of impurities from terephthalic acid wherein an aqueous solution of a salt of terephthalic acid is extracted with n-butanol or benzyl alcohol at a temperature of about 0.degree. C. (32.degree. F.) to about 150.degree. C. (302.degree. F.). The resulting phases are separated to provide an aqueous salt solution of increased purity, and the terephthalic acid is precipitated from solution by acidification.
In U.S. Pat. No. 3,746,750, Stautzenberger, et al, disclose a process for purifying relatively insoluble acids, such as terephthalic acid, by forming a solution of the acid in an aqueous solution of weak acid salts of lithium, a tertiary ammonium ion, or a quaternary ammonium ion, treating the resulting solution with a reagent, such as an oxidizing agent, to reduce the impurities that are present, and recrystallizing the purified acid from solution.
In U.S. Pat. No. 4,500,732, Petty-Weeks, et al, disclose a process for removing p-toluic acid from purified terephthalic acid, wherein p-toluic acid is extracted from the aqueous terephthalic acid-water phase with p-xylene, and the p-toluic acid and p-xylene are recycled to the p-xylene oxidation reactor.
Now there has been developed a process for the purification of organic polycarboxylic acids that are immiscible or partially miscible with water, which process employs steam distillation.